To determine the relative humidity in the given scenario, we need to understand the relationship between the actual vapor pressure and the saturation vapor pressure at a specific temperature. Let's break down the problem step-by-step. ### Step 1: Understanding Saturation Vapor Pressure (SVP) Saturation vapor pressure is the pressure exerted by water vapor in the air when it is in equilibrium with liquid water at a given temperature. The table provided shows the saturation vapor pressures (SVP) at various temperatures in degrees Celsius (°C). ### Step 2: Identify the Given Values From the table: - At 20°C, the saturation vapor pressure (SVP) is **17.50 mmHg**. - The actual vapor pressure (AVP) in the town at 20°C is given as **10 mmHg**. ### Step 3: Calculate Relative Humidity (RH) Relative humidity is defined as the ratio of the actual vapor pressure to the saturation vapor pressure, expressed as a percentage. The formula for relative humidity is: \[ \text{Relative Humidity (RH)} = \left( \frac{\text{Actual Vapor Pressure (AVP)}}{\text{Saturation Vapor Pressure (SVP)}} \right) \times 100\% \] ### Step 4: Plug in the Values Now, we can substitute the values we have into the formula: \[ \text{RH} = \left( \frac{10 \text{ mmHg}}{17.50 \text{ mmHg}} \right) \times 100\% \] ### Step 5: Perform the Calculation 1. Calculate the fraction: \[ \frac{10}{17.50} \approx 0.5714 \] 2. Convert to percentage: \[ 0.5714 \times 100\% \approx 57.14\% \] ### Step 6: Round the Result Rounding 57.14% gives us approximately **57.0%**. ### Conclusion Thus, the relative humidity in the town at 20°C with an actual vapor pressure of 10 mmHg is approximately **57.0%**. Therefore, the correct answer is **B. 57.0%**. ### Explanation of Other Options - **A. 170.0%**: This value is not possible because relative humidity cannot exceed 100%. It suggests that the actual vapor pressure is greater than the saturation vapor pressure, which is not physically feasible. - **C. 17.5%**: This value is misleading as it appears to be the saturation vapor pressure at 20°C, not the relative humidity. It does not represent the actual conditions. - **D. 10.0%**: This option represents the actual vapor pressure as a percentage of the saturation vapor pressure, but it does not account for the saturation condition. It is incorrect as it does not reflect the relationship needed to calculate relative humidity. ### Revision Summary - Relative humidity is calculated using the formula: \( \text{RH} = \left( \frac{\text{AVP}}{\text{SVP}} \right) \times 100\% \). - At 20°C, the saturation vapor pressure is 17.50 mmHg, and the actual vapor pressure is 10 mmHg. - The calculated relative humidity is approximately 57.0%. - Relative humidity cannot exceed 100%, and values like 170.0% or 10.0% do not accurately represent the conditions described.